A high frequency power supply device that supplies a high frequency power to a plasma load or the like, for example, as disclosed in Patent Literature 1, includes a DC power supply unit that can control an output by a predetermined amount of operation (for example, a duty ratio of PWM control performed by a DC/DC converter), a high frequency power generation unit having a high frequency power amplification unit which generates a high frequency power that is supplied to a load using an output voltage of the DC power supply unit as a power supply voltage, and a control unit controlling the high frequency power generation unit.
The DC power supply unit includes, for example, a rectification circuit (converter) converting an output of a commercial power supply into a DC output, an inverter converting an output of the rectification circuit into an AC voltage, and a DC/DC converter having a rectification and smoothing circuit rectifying and smoothing an output of the inverter.
The high frequency power amplification unit includes a power amplifier amplifying a high frequency signal using the output voltage of the DC power supply unit as a power supply voltage, and an inverter converting the output of the DC power supply unit into a high frequency output. The high frequency power that is obtained from the high frequency power generation unit that is composed of the DC power supply unit and the high frequency power amplification unit is supplied, as needed, to a load such as a plasma load through an impedance matching unit.
The control unit that controls the high frequency power generation unit includes a high frequency power detection unit detecting a level of the high frequency power at an output side of the high frequency power generation unit in each detection timing, which is a timing that comes in each set control period, in order to obtain the high frequency power that is targeted for control in each control period, and detecting a moving mean value that is calculated from n (n is an integer that is equal to or larger than 2) detection data detected in recent n detection timings as a mean value of the high frequency power that is targeted; an operation amount calculation unit setting a size of a variable for determining a level of the high frequency power output from the high frequency power generation unit as an operation amount of the high frequency power generation unit and calculating the operation amount that is needed to keep the mean value of the high frequency power that is targeted for control and detected by the high frequency power detection unit to a setting value; and a control signal output unit outputting in each control period a control signal that is given to the high frequency power generation unit in order to take the operation amount of the high frequency power generation unit as the operation amount calculated by the operation amount calculation unit.
The operation amount of the high frequency power generation unit is a variable that determines the output of the DC power supply unit or a gain of the power amplifier that constitutes the high frequency power amplification unit 3. For example, in the case where the DC power supply unit is composed of the DC/DC converter having the above-described configuration, the duty ratio of the PWM control of the inverter that converts the output of the rectification circuit into the AC voltage may be the operation amount.
In the case of performing a control for keeping the output of the high frequency power supply device to the setting value, a control to keep the level (instantaneous value) of the high frequency power, which is detected in the control period and is targeted for control, to the setting value is not performed, but a control to detect the mean value of the output level of the high frequency power supply device and to keep the mean value to the setting value is performed. As a method for this, a method for controlling the high frequency power generation unit is used so as to detect the level of the high frequency power that is targeted for control in each control period, to consider the moving mean value of the level of the high frequency power obtained from the recent detection data as the mean value of the high frequency power, and to keep this mean value to the setting value.
In a plasma processing device that performs various kinds of processes using plasma with respect to a work piece such as a semiconductor or liquid crystals, plasma is generated by applying high frequency power between electrodes installed in a process chamber, and a high frequency power supply device for giving a bias power to the plasma is needed to perform various kinds of control such as control of ion energy or the like in addition to the high frequency power for generating the plasma from the need of planning miniaturization and speedup of the processing. The high frequency power supply device for supplying the high frequency power for generating the plasma and the high frequency power supply device for supplying the high frequency power for bias have different frequencies. The output frequency of the high frequency power for generating the high frequency power for generating the plasma is, for example, in the frequency range neighboring several tens to several hundreds of MHz, and the output frequency of the high frequency power for generating the high frequency power for bias is in the relatively low frequency range of several tens of kHz to several MHz. In Patent Literature 1, as illustrated in FIG. 7, a power supply system for supplying power from first and second high frequency power supply devices A and B having different output frequencies to a plasma load C is described.
The power supply system for supplying a high frequency power to a load such as the plasma load C may supply a high frequency power having a non-modulated consecutive voltage waveform to the load C or may supply a high frequency power having a modulated voltage waveform through a pulse waveform by a demand of the load side.
Patent Literature 1: Japanese Patent Application Publication No. 2009-238516A
In the system in which the first high frequency power supply device A and the second high frequency power supply device B are installed as illustrated in FIG. 7 to simultaneously supply the power to the plasma load C, a high frequency power of approximately a constant level, of which the output frequency is f1 (for example, f1=3.2 MHz) and of which the voltage V1 forms a consecutive waveform (non-modulated waveform), may be supplied from the first high frequency power supply device A to the plasma load C as illustrated in FIG. 8A, and a high frequency power, of which the output frequency is f2 (for example, f2=60 MHz) and of which the level of the voltage V1 is changed in each period T3 (f=1/f3) since the high frequency power has been modulated into a pulse waveform having the frequency f3 (for example, f3=10 kHz to 90 kHz), may be supplied from the second high frequency power supply device B to the plasma load C as illustrated in FIG. 8B. In this case, fluctuation (slow level change of the low frequency) may occur in the mean value of the output of the first high frequency power supply device A that outputs the high frequency power of the consecutive waveform.
In the power supply system illustrated in FIG. 7, the high frequency power of the consecutive waveform (non-modulated waveform) may be supplied from the first high frequency power supply device A to the plasma load C, and the pulse-modulated high frequency power may be supplied from the second high frequency power supply device B to the plasma load C. In this case, if the modulated frequency of the high frequency power that is given from the second high frequency power supply device B to the plasma load C is changed, the accuracy of output control for keeping the output of the first high frequency power supply device A to the setting value may deteriorate.
In order to perform fine processing of a semiconductor or the like at high accuracy, it is needed to perform the control for keeping the mean value of the high frequency power that is supplied to the plasma load to the setting value at high accuracy, and thus it is needed to avoid change of the high frequency power (mean value) that is supplied to the load or deterioration of the accuracy of the output control as much as possible.
The high frequency power supply device according to the present invention is, as illustrated in FIG. 7, a high frequency power supply device that generates a high frequency power of the consecutive waveform (non-modulated waveform) among a plurality of high frequency power supply devices that simultaneously supply the high frequency powers to the load C.